Project Summary: In Phase I we developed a model system and a prototype Salt Sensitivity Assay to establish proof-of-principle . In Phase II we propose the evaluation of the prototype that will quantitatively measure our biomarker in the target population. An ideal biomarker for salt sensitivity would be one that is linked to the underlying cause of salt sensitivity and not disease symptoms. It is our hypothesis that this biomarker can be accurately measured using a monoclonal antibody-based direct quantitative ELISA. The assay will allow physicians to identify salt sensitivity in newly diagnosed hypertensive patients so that appropriate therapy can begin as early as possible. The information gained from this accurate screening test will lead to basic research investigations of the biological mechanisms underlying salt sensitivity and its pathophysiological consequences such as hypertension, CHF, renal disease, and edema. We request Phase II support so that we can evaluate our prototype Salt Sensitivity Assay in a pivotal study with the ultimate goal of obtaining FDA approval. In addition, our proposal also addresses several research questions and explores an exciting new secondary application of our assay in the assessment of renal function. Project Narrative Hypertension affects almost 50 million people in the United States, which places them at higher risk for chronic renal failure and cardiovascular disease. Of those affected, about half are salt-sensitive. We will develop an ELISA for hypertensive people that can be used to distinguish between salt sensitive and salt resistant individuals.